1) Field of the Invention
This invention relates generally to apparatuses and methods for injecting fluids and more specifically to an injector and associated method for injecting combustion fluids into a combustion chamber.
2) Description of Related Art
The combustion of carbon-based compounds, or carbonaceous fuels, is widely used for generating kinetic and electrical power. In one typical electric generation system, a carbonaceous fuel such as natural gas is mixed with an oxidizer and combusted in a combustion device called a gas generator. The resulting combusted gas is discharged to, and used to rotate, a turbine, which is mechanically coupled to an electric generator. The combusted gas is often discharged to one or more additional combustion devices, called reheaters, where the combusted gas is mixed with additional fuel and/or oxidizer for subsequent combustion.
Gas generators and reheaters are generally similar combustion devices, but gas generators have traditionally been used as initial combustion devices and reheaters have traditionally been used as secondary combustion devices that recombust a gas after the gas has gone through an initial combustion device. Gas generators typically combust at least some liquid combustion components, e.g. liquid water, while reheaters typically combust only gases including, for example, steam. Therefore, the volumetric expansion of the combustion gases in a typical gas generator is higher than that of a reheater. Further, the pressure drop across the injector system of a gas generator is typically higher than that of a reheater.
The combustion in both gas generators and reheaters results in high temperatures and pressures. In some systems, pure oxygen is used as the oxidizer to eliminate the production of nitric oxides (NOx) and sulfur oxides (SOx) that typically result from combustion with air. The temperature in such an oxygen-fed system can be especially high, sometimes exceeding 5000xc2x0 F. Such extreme conditions increase the stress on components in and around the combustion chambers, increasing the likelihood of failure of such components and decreasing their useful lives accordingly.
Injectors are used to inject the combustion components of fuel, oxidizer, and/or recycled gases into the combustion chambers of the gas generator and reheaters. Because of their position proximate to the combustion chambers, the injectors are subjected to the extreme temperatures of the combustion chamber. Additionally, the injectors may be heated by the passage of preheated combustion components therethrough. Failure of the injectors due to the resulting thermal stress caused by overheating increases operating costs, increases the likelihood of machine downtime, and presents an increased danger of worker injury and equipment damage.
One proposed injector incorporates a mixer for combining a coolant with the fuel before the fuel is combusted. For example, U.S. Pat. No. 6,206,684 to Mueggenburg describes an injector assembly 10 that includes two mixers 30, 80. The first mixer 30 mixes an oxidizer with a fuel, and the second mixer 80 mixes coolant water with the prior mixed fuel and oxidizer. The mixture then flows through a face 121 to a combustion chamber 12 for combustion. The coolant water reduces the temperature of combustion of the fuel, easing the stress on the system components. One danger presented by such a design is the possibility of xe2x80x9cflashback,xe2x80x9d or the combustion flame advancing from the combustion chamber into the injector. Flashback is unlikely in an injector outlet that has a diameter smaller than the mixture""s xe2x80x9cquenching distancexe2x80x9d. Thus, flashback can be prevented by limiting the size of the injectors. Undesirably, however, a greater number of small injectors is required to maintain a specified flow rate of the combustion mixture. The increased number of injectors complicates the assembly. Small injectors are also typically less space-efficient because the small injectors require more space on the face than would a lesser number of large injectors that achieve the same flow rate. Space on the face is limited, so devoting more space to the injectors leaves less space for other uses, such as devices for injecting coolant into the combustion chamber.
Because sufficient quantities of coolant sometimes cannot be injected from the face, coolant must be injected further downstream. The injection of liquid coolant presents a danger to turbine blades located downstream from the combustion device. If the coolant is not fully vaporized before reaching the turbine, droplets of liquid coolant can damage the turbine blades. Injection of large volumes of a liquid coolant near the turbine blades can increase the likelihood of droplets progressing to the turbine blades, and decrease the useful life of the blades. Turbine blades are sometimes protected by splash plates, which provide a physical barrier to prevent the progression of liquid coolant. However, splash plates add complication to the system, requiring additional service and increasing the cost of the system. Splash plates can also interfere with the flow of gas through the combustion chamber and turbine, and are sometimes not fully effective in protecting the turbine blades.
Additionally, small injectors are subject to further complications due to their size. For example, small passages and outlets in the injectors can become blocked by particulates present in the fuel, oxidizer, or coolant. Thus, the reactants must be carefully filtered before passing through the injector. The need for filters also increases the complexity and cost of the system, as well as the likelihood of failure.
Thus, there exists a need for an apparatus and method for injecting fluid components of combustion into a combustion chamber. The injector and method should prevent liquid water from progressing to downstream turbine blades and should minimize the likelihood of flashback. Preferably, the injector should not be overly complex and should not require stringent filtering of the combustion components. The injector and method should be adaptable for use with gas generators and reheaters of various sizes. Further, the injector and method should facilitate efficient combustion, even at varying flow rates and limit the temperature of the injector to decrease thermal stress, likelihood of failure, and operating costs.
The present invention provides an injection system, an injector, and an associated method for injecting combustion fluids into a combustion chamber. Each injector injects an oxidizing fluid formed from a mixture of steam and oxygen to impinge on, and mix with, a stream of fuel in a combustion chamber. Mixing the oxidizing fluid and fuel in the combustion chamber decreases the likelihood of flashback, even with relatively large streams of fuel. Any number of injectors can be included on a faceplate of an injection system for a gas generator or reheater, and the thorough mixing provided by the injector also increases the efficiency of the combustion, even at low flow rates. Further, the flexibility in the size of the injectors also increases the potentially available space on the faceplate for coolant injectors. Locating the coolant injectors at the faceplate reduces the likelihood of coolant droplets progressing through the combustion chamber to the turbine.
According to one embodiment of the present invention, the injection system includes a first faceplate and a plurality of injectors extending through the first faceplate. The faceplate has an inlet side and an outlet side that faces the combustion chamber. Each of the injectors has a fuel bore that extends from a fuel bore inlet to a fuel bore outlet located at an outlet side of the injector. The diameter of the fuel bore can converge in a direction from the fuel bore inlet to the fuel bore outlet. A swirler chamber defined by the injector has at least one inlet for receiving steam and oxygen, which are preferably mixed before entering the inlet. A converging channel extends from the swirler chamber to an oxidizing fluid outlet located on the injector outlet side. The converging channel of each injector is configured relative to the fuel bore such that oxidizing fluid that exits through the oxidizing fluid outlet impinges on a stream of fuel in the combustion chamber following exit of the stream of fuel from the fuel bore.
According to one aspect of the invention, a center of each of the injectors is located at least 1 inch from the centers of the other injectors. A source of carbonaceous fuel can be fluidly connected to each of the fuel bore inlets of the injectors, and each inlet of the swirler chambers can be fluidly connected to a source of oxidizing fluid comprising steam and oxygen substantially free of nitrogen and sulfur. In one embodiment, the oxidizing fluid comprise at least 50% steam as measured on a weight basis.
According to another aspect, each of the swirler chambers defines a slot that extends circumferentially around the fuel bore of the respective injector. The converging channel of the injector can converge at an angle of between about 10xc2x0 and 45xc2x0 relative to the fuel bore such that the oxidizing fluid exiting each injector impinges on the stream of fuel in the combustion chamber. The converging channel can also converge toward the respective fuel bore such that the oxidizing fluid exiting the injector impinges on the stream of fuel in the combustion chamber in a region located within about 2 inches of the first faceplate. The inlets of the swirler chambers can extend in a radial direction from the swirler chambers to the outside of the injector bodies such that fluid flowing into each of the swirler chambers through the swirler chamber inlets swirls in a circumferential direction around the respective fuel bore. Further, a vane can be disposed in each of the swirler chambers and configured to induce a swirling motion to fluid flowing through the respective swirler chamber.
According to another aspect of the present invention, a plurality of water injectors are configured to inject water into the combustion chamber from the first faceplate. The water injectors can be configured such that the combustion fuel travels a distance of at least about 10 inches from the first faceplate before mixing with the water, and the water injectors can be fluidly connected to at least one coolant chamber defined by the first faceplate. In one aspect, a second faceplate faces the inlet side of the first faceplate, and the two faceplates define at least one coolant chamber therebetween, the coolant chamber being configured to receive and circulate a coolant fluid for cooling the faceplate. Further, an interpropellant plate can face the second faceplate, and the interpropellant plate and the second faceplate can define at least one oxidizing fluid chamber fluidly connected to the at least one inlet of the swirler chambers of the injectors.
In another aspect, the combustion chamber defines a passage from the outlet side of the first faceplate to a turbine, and the passage is uninterrupted by splash plates. The injection system can also include at least one water injector configured to inject water into the combustion chamber at a location downstream of the faceplate.
The present invention also provides an injector for injecting fluids into a combustion chamber. The injector has an injector body with an inlet side and outlet side. A fuel bore extends from a fuel bore inlet to a fuel bore outlet located on the outlet side. The fuel bore can converge in a direction from the fuel bore inlet to the fuel bore outlet. A swirler chamber is defined by the injector body and has at least one inlet for receiving steam and oxygen. A converging channel extends from the swirler chamber to an oxidizing fluid outlet located at the outlet side of the injector body. The converging channel is configured relative to the fuel bore such that oxidizing fluid exiting the injector through the oxidizing fluid outlet impinges on a stream of fuel in the combustion chamber flowing from the fuel bore through the fuel outlet.
The swirler chamber can extend circumferentially about the fuel bore such that the steam and oxygen can flow circumferentially in the swirler chamber. The converging channel can converge at an angle of between about 10xc2x0 and 45xc2x0 relative to the fuel bore such that the oxidizing fluid exiting the injector impinges on the stream of fuel in the combustion chamber. The converging channel can also be configured such that the oxidizing fluid impinges on the stream of fuel in the combustion chamber in a region located within about 2 inches of the fuel bore outlet.
In one embodiment, each of the inlets of the swirler chamber extends in a radial direction from the swirler chamber to the outside of the injector body such that fluid flowing into the swirler chamber through the swirler chamber inlets swirls in a circumferential direction around the fuel bore. One or more vanes can also be disposed in the swirler chamber, extending in a circumferential direction around the fuel bore and configured to induce a swirling motion to fluid flowing through the swirler chamber.
The present invention also provides a method of injecting and combusting combustion fluids in a combustion chamber. The method includes injecting a combustion fuel such as a carbonaceous gas into the combustion chamber. An oxidizing fluid comprising oxygen and steam is injected into the combustion chamber such that the oxidizing fluid impinges on the combustion fuel in the combustion chamber. The oxidizing fluid can be substantially free of nitrogen and sulfur, and the oxidizing fluid can include at least 50% steam as measured on a weight basis. The method also includes combusting the combustion fuel with the oxidizing fluid. The steam can be used to limit the flame temperature to below about 4000xc2x0 F.
In one aspect of the invention, the combustion fuel and oxidizing fluid is injected through a plurality of injectors, and a center of each of the injectors is located at least 1 inch from the centers of the other injectors.
The steam and oxygen can be mixed by swirling the oxygen and steam in a circumferential direction within the injector. The combustion fuel can be injected through a fuel bore outlet and the oxidizing fluid can be injected at an angle of between about 10xc2x0 and 45xc2x0 relative to the fuel bore such that the oxidizing fluid impinges on the combustion fuel in the combustion chamber. The oxidizing fluid can also be injected to impinge on the combustion fuel in the combustion chamber in a region located within about 2 inches of the fuel bore outlet.
In another aspect of the invention, the combustion fuel and a coolant are injected into the combustion chamber through the faceplate. The coolant can be injected in a direction such that the combustion fuel travels a distance of at least about 10 inches into the combustion chamber before mixing with the coolant. Further, the coolant can be circulating through a faceplate cooling chamber defined by the faceplate.
Thus, the present invention provides a system, injector, and method for injecting fluid components of combustion into a combustion chamber. The injectors control the combustion temperature by mixing steam with oxygen and impinging the resulting oxidizing fluid on the fuel in the combustion chamber, thus limiting thermal stress of system components. Mixing the oxidizing fluid and fuel in the combustion chamber minimizes the risk of flashback and allows the use of larger streams of fuel. The system can include any number of injectors, and provides efficient combustion even at low flow rates in a gas generator or a reheater. Complexity and risk of turbine damage are decreased by locating coolant injectors at the faceplate.